TfL said it is investigating and apologised to Young for his experience, adding that any form of hate crime is "completely unacceptable and will not be tolerated".

Young also appealed to Mayor of London Sadiq Khan for help in tracking down the bus driver, adding that he didn't want to start a "witch hunt" but just wanted an "apology".

He tweeted: "TfL been great at reacting to my tweet . All I need is an apology – no witch hunt . To be called a poofter isn't the nicest thing and it reminds me what a vile thing prejudicial language is to try and shame others. I can take action, many young people can't."

Bus drivers are not directly employed by TfL, but instead work for private companies that win contracts to run services.

In a statement, TfL's director of enforcement Steve Burton said: "We're very sorry to hear of Will Young's experience, and are looking into it urgently. Any form of hate crime is completely unacceptable and will not be tolerated.

"Everyone has the right to travel without fear of abuse or intimidation and if anyone witnesses or is victim to hate crime they should report it immediately."

It is not the first time Young has been subject to homophobic attacks since finding fame on Pop Idol in 2002.

Last year he revealed he had been threatened with a knife and had publicly confronted homophobia.

Will had told the i newspaper: "I've had to run away from knife threats, hide in shops. I've also taken people on."

The singer also recalled an incident on a street in Oxford where he confronted a group of people who were being homophobic.

"The whole of the street turned against them and I think that was a palpable sign of how it's simply not tolerated now," he said.

He added: "People [who bully] just need to be educated, they don't need to be punished."

TfL been great at reacting to my tweet . All I need is an apology - no witch hunt . To be called a poofter isn't the nicest thing and it reminds me what a vile thing prejudicial language is to try and shame others. I can take action, many young people can't